1. Field of the Invention
The present invention relates to a water heater in which a circulation line is provided in a water heating part for circulating hot water, and in which operation of a heat pump and a circulation pump is controlled according to temperature of the circulated hot water, elapsed time, etc.
2. Description of the Related Art
Conventionally, there is a water heater in which a pump is individually disposed in a hot water supply pipe and hot water is circulated therein. Thus, hot water of desired temperature is available instantaneously. In a case of such circulation, the pump is turned ON/OFF by a switch including a temperature sensor so as to supply hot water at prescribed setting temperature, for example, the switch is provided with a thermostat or a timer.
A controller for pump control is on the market. This controller detects temperature on a pipe or water temperature in the pipe by, for example, being attached to the pipe and stops combustion in a heat pump.
If the above controller is not disposed in the structure of circulating hot water, the endurance of a water heater may be decreased because, for example, a pump operates continuously.
It is known as such a water heater in which hot water is circulated in a circulation line that a circulation pump and a heater are provided in a circulation line and operation of the circulation pump and the heater is stopped according to the rise in temperature of the circulated hot water (for example, Japanese Laid-open Utility Model Publication No. 63-123915).
It is also known that a sensor detecting the minimum temperature is provided in a circuit and when detected temperature goes down to the freezing temperature, a pump and heating means are operated (for example, Japanese Laid-open Patent Publication No. 63-207948.)
Components other than a heat pump, such as a tank and a temperature detector, or a controller that controls these components are required to be disposed for making an instantaneous water heating unit so that heated hot water is available instantaneously as soon as a hot water supply operation is performed. This disposition complicates the structure of a water heater.
When the outside air is low temperature, hot water is circulated in a circulation line so as not to freeze the circulation line. There is a problem that the structure of a water heater is complicated because individual control means is provided for a planned circulation process.
Concerning such problems, there is no disclosure or suggestion thereof in Japanese Laid-open Utility Model Publication No. 63-123915 and Japanese Laid-open Patent Publication No. 63-207948, and no disclosure or suggestion about the structure etc. for solving them is presented.